commit 4d8c8bd6 upstream.

Occasionaly PV guests would crash with:

pciback 0000:00:00.1: Xen PCI mapped GSI0 to IRQ16
BUG: unable to handle kernel paging request at 0000000d1a8c0be0
.. snip..
  <ffffffff8139ce1b>] find_next_bit+0xb/0x10
  [<ffffffff81387f22>] cpumask_next_and+0x22/0x40
  [<ffffffff813c1ef8>] pci_device_probe+0xb8/0x120
  [<ffffffff81529097>] ? driver_sysfs_add+0x77/0xa0
  [<ffffffff815293e4>] driver_probe_device+0x1a4/0x2d0
  [<ffffffff813c1ddd>] ? pci_match_device+0xdd/0x110
  [<ffffffff81529657>] __device_attach_driver+0xa7/0xb0
  [<ffffffff815295b0>] ? __driver_attach+0xa0/0xa0
  [<ffffffff81527622>] bus_for_each_drv+0x62/0x90
  [<ffffffff8152978d>] __device_attach+0xbd/0x110
  [<ffffffff815297fb>] device_attach+0xb/0x10
  [<ffffffff813b75ac>] pci_bus_add_device+0x3c/0x70
  [<ffffffff813b7618>] pci_bus_add_devices+0x38/0x80
  [<ffffffff813dc34e>] pcifront_scan_root+0x13e/0x1a0
  [<ffffffff817a0692>] pcifront_backend_changed+0x262/0x60b
  [<ffffffff814644c6>] ? xenbus_gather+0xd6/0x160
  [<ffffffff8120900f>] ? put_object+0x2f/0x50
  [<ffffffff81465c1d>] xenbus_otherend_changed+0x9d/0xa0
  [<ffffffff814678ee>] backend_changed+0xe/0x10
  [<ffffffff81463a28>] xenwatch_thread+0xc8/0x190
  [<ffffffff810f22f0>] ? woken_wake_function+0x10/0x10

which was the result of two things:

When we call pci_scan_root_bus we would pass in 'sd' (sysdata)
pointer which was an 'pcifront_sd' structure. However in the
pci_device_add it expects that the 'sd' is 'struct sysdata' and
sets the dev->node to what is in sd->node (offset 4):

set_dev_node(&dev->dev, pcibus_to_node(bus));

 __pcibus_to_node(const struct pci_bus *bus)
{
        const struct pci_sysdata *sd = bus->sysdata;

        return sd->node;
}

However our structure was pcifront_sd which had nothing at that
offset:

struct pcifront_sd {
        int                        domain;    /*     0     4 */
        /* XXX 4 bytes hole, try to pack */
        struct pcifront_device *   pdev;      /*     8     8 */
}

That is an hole - filled with garbage as we used kmalloc instead of
kzalloc (the second problem).

This patch fixes the issue by:
 1) Use kzalloc to initialize to a well known state.
 2) Put 'struct pci_sysdata' at the start of 'pcifront_sd'. That
    way access to the 'node' will access the right offset.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>